Biodegradable plastic molded article

ABSTRACT

A biodegradable plastic article molded of a mixture comprising the following components: 
     (A) a biodegradable plastic at 98 to 59% by weight, 
     (B) a dry powder of a water-swelling fiber at 1 to 40% by weight, and 
     (C) a fertilizer powder at 1 to 40% by weight 
     (wherein the sum of (B) and (C) is from 2 to 41% by weight). This biodegradable plastic article can improve biodegradability of the biodegradable plastics and make it possible to regulate the rate of biodegradation thereof.

DESCRIPTION

1. Technical Field

The present invention relates to a biodegradable plastic molded articleand more particularly to a biodegradable plastic molded article with ahigh biodegradation rate.

2. Background Art

The demand for biodegradable plastics which degrade in the environmentincreases due to environmental problems faced by the society.Biodegradable plastics which have already been developed are classifiedinto the following four categories, which partially overlap each other.

(a) naturally-occurring polymers consisting of polysaccharides such asstarch,

(b) microbial polyesters using the biological activities ofmicroorganisms (polyhydroxyalkanoates and the like),

(c) usual plastics added with degradation accelerators, that is,mixtures having accelerated degradation characteristics, and

(d) chemosynthetic compounds including aliphatic polyesters and thelike.

The biodegradable plastics have been used as raw materials forthrow-away articles or used for articles which do not need to usuallycarry heavy loads based on the individual characteristics of thesedifferent materials. Examples of the above-mentioned application includeagricultural articles such as films, sheets, fastening screws, plantingpots, and sacks; daily necessities and table wares such as trays, cases,and straws; certain medical articles; and sporting goods. However,applicability of the biodegradable plastics is still restrictive. Theinfluence thereof on the overall plastic industry is also restricted.

The review of “the present state of technology” concerningmacromolecules which degrade in the environment is shown in“Encyclopedia of Chemical Technology, the fourth edition” Vol. 19,968-1004, published by John Wiley and Sons Corporation, 1996. The abovewhole teaching is hereby incorporated into the present description byreference. In addition, the review of the manufacturing method and thetest method utilized at present is shown in “Encyclopedia of ChemicalTechnology, the fourth edition” Vol. 19, 290-347, published by JohnWiley and Sons Corporation, 1996. The above whole teaching is herebyincorporated into the present description by reference.

Although the biodegradable plastics are generally full of promise tosolve the plastic disposal problems, there are also some difficulties. Abiodegradation rate may be slower than the expected rate due to kindsand ratios of biodegradable plastic contents and also due to differencesof the environment where the biodegradable plastics are disposed. Inaddition, another problem is that when a thickness of molded articlesincluding biodegradable plastics increases, the biodegradability thereofreduces. Furthermore, the life of the molded articles including thebiodegradable plastics may be shorten compared with the desired life dueto insect pests. Further serious problems are that functions thereof arelimited to optimally narrow objectives, or a large part of themacromolecules thereof are specially prepared so as to act certain partsduring a manufacturing step. Partially degradable plastics includingnon-biodegradable plastics have not satisfactory quality. Therefore,improvement in biodegradability of all plastics with maintaining beneficcharacteristics of each biodegradable plastic is remarkably useful.

A method for achieving this object is using additives which makeplastics to be easily degraded in the environment instead of fillerswhich are usually used now. At present, the additives to plastics areemployed in order to give favorable characteristics to the plastics. Forexample, additives are used for giving characteristics such as strength,hardness, flexibility, and color.

The review concerning characteristics, application, and toxicity of theadditives to plastics in detail is shown in “Chemical Additives for thePlastics Industry”, published by Radian Corporation and Noyes DataCorporation, N.J., U.S.A., 1987. The above whole teaching is herebyincorporated into the present description by reference.

One candidate which improves the degradability in the environment of theadditives to the plastics is biomaterials such as plant fibers and woodpowders. Since the plant fibers alone and wood powders include lignin(phenolic polymer) and have repellent nature to insects, theseutilization reduces biodegradability.

In contrast, the inventors of the present invention have found that whenthe dry powders of the fibers included in coconut mesocarp are mixedwith biodegradable plastics, the biodegradability thereof can beincreased (JP-A-9-263700).

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a biodegradable plasticmolded article having further superior biodegradability to theconventional art.

Another object of the present invention is to accelerate thebiodegradability of the conventional biodegradable plastics preferablywithout deteriorating the processing characteristics such as goodmolding, extrusion, blow molding, foam molding, inflation molding andother molding methods.

Still another object of the present invention is to further improve thebiodegradability of the conventional biodegradable plastics, andsimultaneously to allow controlling a biodegradation rate of thebiodegradable plastic molded articles.

To address the above-described problems, the inventors of the presentinvention performed careful examinations. As a result, the inventors ofthe present invention have found that when dry powders of water-swellingfibers and fertilizer powders are mixed with biodegradable plastics, thebiodegradability thereof can be accelerated, so that the presentinvention has been completed

That is, an aspect of the present invention is a biodegradable plasticarticle molded of a mixture including the following components:

(A) biodegradable plastics at 98 to 59% by weight,

(B) a dry powder of a water-swelling fiber at 1 to 40% by weight, and

(C) fertilizer powder at 1 to 40% by weight

(wherein the sum of (B) and (C) is from 2 to 41% by weight).

In one embodiment, the present invention includes a biodegradableplastic molded article, wherein the dry powders of the water-swellingfibers include dry powders of coconut mesocarp fiber residues.

In another embodiment, the present invention includes a biodegradableplastic molded article, wherein the dry powders of the coconut mesocarpfibers residues are obtained by drying the fiber residues to a watercontent of about 10% by weight in which the residues are derived from afiber components of the coconut mesocarp and contaminants includingsalts and tannin are essentially removed, by compressing into powdershaving a particle diameter ranging from 1 to 80 micron, and by drying toa water content of less than 3% by weight.

In still another embodiment, the present invention includes abiodegradable plastic molded article, wherein the biodegradable plasticis selected form the group consisting of aliphatic polyesters,macromolecular polysaccharides, and microbial polyesters.

In still another embodiment, the present invention includes abiodegradable plastic molded article, wherein the fertilizer is selectedform the group consisting of nitrogenous fertilizers, phosphatefertilizers, potassium fertilizers, and fertilizers includingdiatomaceous.

Another aspect of the present invention is a biodegradable plasticarticle molded of a mixture including the following components:

(A) biodegradable plastics at 97 to 58% by weight,

(B) dry powders of water-swelling fibers at 1 to 40% by weight,

(C) fertilizer powders at 1 to 40% by weight, and

(D) a component selected form the group consisting of surfactants,stains, and agricultural chemicals at 1 to 10% by weight (wherein thesum of (B), (C), and (D) is from 3 to 42% by weight).

The present invention will be described in detail below.

The biodegradable plastic molded articles in accordance with the presentinvention show accelerated biodegradability by mixing dry powders ofwater-swelling fibers and fertilizer powders with biodegradableplastics. In addition, the adjustment of the mixed composition cancontrol a degradation rate.

First, the components of the biodegradable plastic molded articles inaccordance with the present invention will be described.

<1> components of the biodegradable plastic molded articles inaccordance with the present invention

(1) Biodegradable plastics ((A) component)

Any biodegradable plastics can be employed in the present invention aslong as the plastics are degraded in the environment, especially inplastics degraded by microorganism activities.

Concrete examples of the above-mentioned biodegradable plastics aremacromolecular polysaccharides, microbial polyesters, aliphaticpolyesters, and the like as described in (a), (b), and (d) in thebackground art. More concrete examples are polylactic acid;polyhydroxyalkanoate (for example, poly(3-hydroxybutyric acid)(PHB),poly(3-hydroxyvaleric acid)(PHV)); lactone resins; polyester resinsobtained from a low molecular weight aliphatic dicarboxylic acid and alow molecular weight aliphatic diol; complexes based on celluloseacetate, polycaprolactone, and the like; and complexes such as denaturedstarch-modified polyvinyl alcohol, other complexes, or the like.

The above-described biodegradable plastics are compounded into a rawmaterial mixture of biodegradable plastic molded articles at 98 to 58%by weight in the present invention. The above-mentioned compoundingamount can be adjustable by adding optional components withoutsacrificing the advantages of the present invention.

(2) Dry powders of water-swelling fibers ((B) component)

The dry powders of water-swelling fibers used in the present inventionare fibrous powders in which the volume thereof increases compared withthat in a dry state, when water is added thereto. The powders are notrestricted, as long as they have the above-mentioned characteristic, donot adversely affect the biodegradability thereof, and are tolerable toplastic molding. Preferably, the powders themselves havebiodegradability. Example of the dry powders of water-swelling fibers ispreferably dry powders of a coconut mesocarp fiber residues (hereafterreferred to as a “coconut powder”). More preferably, the dry powders ofwater-swelling fibers is obtained by drying the fiber residues to awater content of about 10% by weight in which the residues are derivedfrom a fiber component of the coconut mesocarp and a contaminantincluding a salt and a tannin is essentially removed, by compressinginto a powder having a particle diameter ranging from one to 80 micron,and by drying to a water content of less than 3% by weight.

Cocos nucifera is a plant classified among Palmales and is widelycultivated in tropical regions. Its fruit (coconut) is utilized in manyways. According to FIG. 1 (A) showing a longitudinal sectional view of acoconut 1, an albumen 1 c which is usually used as coconut oil, foods,or drug materials and typically has a thickness ranging from 10 to 20 mmis seen in the sidecoconut 1. Usually, a hard wooden mesocarp 1 b knownas an investment has a thickness ranging from 2 to 6 mm. The investmentof the coconut is useful for manufacturing industrial grade and highquality activated carbon. A mesocarp 1 a called parisarc forms largestregion of the coconut and has a typical thickness ranging from 30 to 40mm. The fibers 2 in the mescarp are mostly used for manufacturingstrings, nets, mats, and ropes at present. Although the fiber residueswhich are generated during manufacturing above are processed intocompressed potting compost and used for soil improvement, they are notusually used for other purposes.

The coconut fibers 2 obtained from the mesocarp 1 a is botanicallyclassified among a sclerenchymatous fiber. According to FIG. 1 (B)showing an enlarged cross-sectional view of the coconut fiber 2, thecoconut fiber 2 is found to constructionally include a lumen membrane 2a, a saw tooth trichome 2 b, a hollow foramen 2 c, and a beard like twig2 d. Usually, the length of the beard like twig 2 d of the coconut fiber2 are about 0.7 mm, and the width thereof is about 20 μm. Physically,the coconut fibers are light, hard, and elastic. In addition, thecoconut fiber is a low thermal conductor, and is resistant to water andair (inorganic and organic industrial material handbook, first edition;p788 written by Shoichiro Nagai, published by Toyo Keizai News, Inc.,Mar. 20, 1960). The above whole teaching is hereby incorporated into thepresent description by reference.

The term “a coconut mesocarp fiber residue” used in the presentdescription means a concept nonrestrictively including coconut fiberfine fragments obtained by finely fragmentizing the above-describedcoconut fiber 2. Concrete example of this coconut mesocarp fiberresidues are fiber residues obtained during manufacturing theabove-mentioned coconut fiber products and the like. Furthermore, thecoconut mesocarp fiber residues include fine fragments which remaincross-sectional forms shown in FIG. 1 (B), beard like twigs 2 d detachedfrom the coconut fiber 2, lumen membrane 2 a fragments, and the like.

The dry powders of a coconut mesocarp fiber residues (coconut powders)used in the present invention are obtained by drying and fragmentizingthe above-described coconut mesocarp fiber residues. The method ofmanufacturing thereof is not particularly restricted, and for example,the powder can be produced as follows.

That is, in order to obtain the coconut powder, the coconut mesocarp isexposed to freshwater for 10 to 16 months so as to dissolve pulpysubstances and only fibers are collected. The obtained fibers areexposed to sunlight for about not less than two years so as to removesalts and tannin included therein. Then, an artificial drying with hotair is conducted for about eight hours so as to reduce a water contentto about 10% by weight, so that fine fragments of fibers, namely thecoconut mesocarp fiber residues are obtained. The residues arecompressed with a pressing machine or the like to a compression ratioranging from 4 to 6:1, and then subjected to a crusher such as a ballmill, hammer mill, and jet mill etc. so as to be crushed and madepowders. Drying and removal of the salts and tannin may be conducted,after fine fragments of the fibers are obtained.

Although a size of the coconut powders is not particularly specified,the particle diameter preferably is set ranging from 1 to 80 μm based onthe appearance of plastic molded articles including therein and anenergy cost required for the crush etc.

Although a degree of dryness of the coconut powders is not particularlyspecified, the coconut powders are preferably dried so as to have awater content at less than 3% by weight in the present invention.Adjustment of the water content of the coconut powders may be conductedat a step for manufacturing the coconut mesocarp fiber residues so as tobe less than 3% by weight. Preferably, the following method is employedas described above. That is, the water content is decreased to about 10%by weight at the step for manufacturing the coconut mesocarp fiberresidues and the coconut mesocarp fiber residues are further dried inthe step to manufacture the coconut powders therefrom so as to be lessthan 3% by weight. Usually, when the coconut powders are dried in thestep to manufacture the coconut powders, hot air or the like is employedafter the size of the coconut powders obtained with the above-describedcrush are adjusted using a screen and the like, if necessary.

The coconut powders produced with the above-described manufacturingmethod including a compression step have a characteristic that whenwater is added therein, the volume increases five to six times. Althoughthe volume of the coconut mesocarp fibers residues becomes one fourth toone sixth due to compression, the compressed fiber residues memorize theform in the natural state. Therefore, this phenomenon is assumed to becaused by the same principle in which when water is added, the cells ofthe lumen membranes 2 a recover in the natural state, so that compressedfiber residues recover in the initial form. In addition, this swellingcharacteristic assumes to significantly accelerate the degradation ofbiodegradable plastics. Furthermore, microorganisms seem to prefer thecomponents of the coconut powders (cellulose component and the like).

The above-described dry powders of water-swelling fibers are compoundedinto a raw material mixture of biodegradable plastic molded articles ina ratio ranging from 1 to 40% by weight in the present invention.However, the compounding ratio can be appropriately adjusted dependingon the amount of other compounding components. For example, thecompounding ratio of the dry powders of water-swelling fibers togetherwith the fertilizer powders (C), described later, is ranging from 2 to41% by weight. In addition, in the case that the raw material mixture ofthe biodegradable plastic molded articles in accordance with the presentinvention are compounded with at least one component (D) selected fromthe group consisting of surfactants, stains, and agricultural chemicals,the sum amount of (c) and (D) is ranging from 3 to 42% by weight.

(3) Fertilizer powders ((C) component)

Fertilizer powders act as auxiliary agent to the growth ofmicroorganisms which effect on biodegradable plastics and accelerate thedegradation thereof. As long as the fertilizer powders have theabove-mentioned characteristic, there is no limitation. Concretely,examples of the fertilizer powders used in the present invention arecarbon sources, nitrogen sources, inorganic components, microdosenutrients, and the like which are usually used for medium for themicroorganisms; and components used as fertilizer for plants and thelike, optional mixtures of these components which take powdery forms, orthose processed to take powdery forms, and the like.

Concrete examples of the above-described fertilizer components arenitrogenous fertilizers in which the main ingredient is a compoundincluding nitrogen such as ammonium nitrate, urea, ammonium sulfate,ammonium chloride, and ammonium phosphate; phosphate fertilizers inwhich the main ingredient is a compound including phosphorous such assuperphosphate and ammonium phosphate; potassium fertilizers in whichthe main ingredient is a compound including potassium such as potassiumchloride and potassium sulfate; fertilizers including diatomaceous asthe main ingredient; and the like. These fertilizer components may beused alone or in combination with two kinds or more.

In this description, a term “fertilizers including diatomaceous” is usedfor the above-mentioned fertilizers including diatomaceous as the mainingredient. Any diatomaceous obtained from marine sediment, mud flatsediment, or lacustrine sediment may be used as diatomaceous in thefertilizers including diatomaceous employed in the present invention. Adiatomaceous field is not also especially restricted. Preferably,diatomaceous with high purity which substantially does not containimpurities such as sand, volcanic ash, clay substances, iron, alkalinesalts, sulfuric acid, and animal and plant fossil except diatomaceous isemployed.

A size of the fertilizer powders is not restricted. A particle diameterpreferably is set ranging from 1 to 80 μm based on the appearance ofplastic molded articles including therein and an energy cost requiredfor the crush etc.

Most of the above-described fertilizer powders are commerciallyavailable as one component or fertilizer containing multi componentscompounded with a lot of components. These commercially availablefertilizer powders can be utilized in the present invention.

When the above-described fertilizers are compounded into biodegradableplastics, the proliferation of microorganisms which involve in thebiodegradation of plastics such as Pseudomonas are accelerated to causethe improvement of the biodegradation rate. In addition, since thediatomaceous is natural organic material, it seems to be useful toaccelerate the biodegradability. Furthermore, the degradation rate canbe adjusted depending on a kind or a compounded amount of the fertilizerpowders.

The above-described fertilizer powders are compounded into the rawmaterial mixture of biodegradable plastic molded articles at 1 to 40% byweight in the present invention. However, the above-mentionedcompounding amount can be fitly adjustable by the compounding amount ofother components as concretely described above item (2).

(4) Other components

In addition to the above-described components, other components may beoptionally compound into the biodegradable plastic molded article in thepresent invention.

For example, since phytogenous pathogenic organisms prefernon-biodegradable plastics (petroleum polyesters) and the like, thenon-biodegradable plastics may be added in order to adjust thedegradation rate.

Furthermore, industry standard plastic additives can be added in orderto obtain the desired characteristics. For example, surfactants may beadded to improve workability, or stains such as a variety of pigmentsmay be added to improve marketability. In addition, agriculturalchemicals may be added in order to protect soil from insect pests, ifnecessary. The characteristics of the basic plastic materials can bemodified by addition of polymerization regulators such as crosslinkingagents, monomer derivatives, heteromonomers, curing agents.

In the present invention, among these optional components, at least onecomponent ((D) component) selected from the group consisting ofsurfactants, stains, and agricultural chemicals is preferablycompounded. The compounding amount of (D) components as the sum amountis usually ranging from 1 to 10% by weight.

Moreover, the well known antioxidants, carbon black (Ketzin carbon),inorganic fillers, slip additives, antiblocking agents and the like maybe added. When these agents are added, the sum added amount thereof canbe reduced from any one or more adding amount of the above-describeditems (A), (B), (C), and (D) without affecting the advantages of thepresent invention.

To increase dispersibility of coconut powders and fertilizer powders inthe biodegradable plastic molded articles, the coconut powders and/orthe fertilizer powders can be subjected to surface treating withcoupling agents such as silane.

<2> Methods of manufacturing the biodegradable plastic molded articlesin accordance with the present invention.

Next, methods of manufacturing the biodegradable plastic molded articlesin accordance with the present invention will be illustrated.

Usually, coconut powders and fertilizer powders are solvently mulled inbiodegradable plastics within the range of the adding ratio according tothe present invention, and pelletized. When at least one componentselected from the group consisting of surfactants, stains, andagricultural chemicals is added into the biodegradable plastic moldedarticles in accordance with the present invention, the component may beadded into the biodegradable plastics together with the coconut powdersand the fertilizer powders within the range of the adding ratioaccording to the present invention during the above-described solventlymulling. The well known mulling apparatus such as a banbary mixer,Henshel mixer, monoaxial muller, multiaxial muller, mixing roll, andkneader is preferably used for the above-described solvently mulling andpelletizing.

Then, molding is performed using the obtained pellets. Methods formolding are not especially restricted, and the usual methods utilizedfor molding plastics are employed. Especially, since the biodegradableplastic molded articles in accordance with the present invention havesuperior biodegradability compared with the conventional ones, moldedarticles having great thickness in addition to films can be obtained.

When the films are produced, the well known film making apparatus suchas the inflation method and T dye method can be employed. Further, adrawing step may be added after the films are produced. Although athickness of the film is appropriately set according to the requiredstrength and required degradation rate due to the use thereof, it isusually set ranging from 10 to 2000 μm.

A biodegradable resin layer in which the coconut powders and thefertilizer powders are not added can be laminated or coated on thesurfaces of the biodegradable plastic molded articles such as films inaccordance with the present invention. In addition, a synthetic resinsuch as polyolefin, polyester, and polyurethane can be laminated orcoated on the surfaces of the films within the range which does notgreatly inhibit the above-described biodegradability.

Examples of the molded articles using a injection molding machine, avacuum forming machine, an extruder, or a blow molding machine areraising seedling pots, piles, ducts, wall materials, platy articles,engineering plastic products, packing materials, agricultural andpiscatorial products, daily necessities, agriculture usable products,architectural materials, and the like. These molded articles can bewidely used as materials and components for civil engineering, medicaluse, sport, greening, and others.

The films among the biodegradable plastic molded articles in accordancewith the present invention can be widely used as compost bags, greeningseeds sacks, garbage bags, shopping bags, a variety of packing films,industrial films, and agricultural films.

For example, when the film is applied to the compost bags, it is usefulin solving the environmental problems, because the bags can be treatedtogether with raw garbage and allowed to return to the realm of nature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (A) is a cross-sectional view of a coconut and FIG. 1 (B) is anenlarged cross-sectional view of the coconut fiber.

FIG. 2 is a graphical representation which compares degradation ratiosover time of films, fragments of seeding pots, and cellulose powder inExample and Comparative examples. A solid line represents the seedingpots in Example, a dotted line represents the cellulose powder, a dottedchain line represents the films in Comparative example 1, and atwo-dotted chain line represents the seeding pots in Comparative example2.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be more concretely described with referenceto the examples below.

PRODUCTION EXAMPLE

After mesocarp and albumen were removed from coconut, the remainingmesocarp was exposed to freshwater for one year to dissolve and removepulpy substances, so that the fiber fraction was collected. The obtainedfibers were exposed to sunlight for three years so as to remove saltsand tannin included therein. An artificial drying with hot air at atemperature of 105° C. was conducted for eight hours so as to reduce awater content to 10% by weight. Then, fine fragments with a lengthranging from 5 to 10 mm, being generated during the production of netswith fibers, were collected. The fine fragments were compressed at acompression ratio of 6:1 using a pressing machine. After the obtainedcompressed substances were crushed by a jet mill and classified using ascreen, coconut powders which passed through a 400 mesh screen wereobtained. The coconut powders were subjected to the artificial dryingwith hot air at a temperature of 70° C. for eight hours, so that thewater content was decreased to 2% by weight. When the obtained coconutpowders were observed with a scanning electron microscope, an averageparticle diameter was confirmed to be about 20 μm.

EXAMPLE

Biodegradable aliphatic polyester which was produced by combined withglycol and aliphatic carboxylic acid at a ratio of 30:70 by weight,respectively (Bionole(r), manufactured by SHOWA KOUBUNSHI Co. LTD.) at90% by weight, the coconut powders obtained in the above Productionexample at 7% by weight, and fertilizer powders (nitrogen: phosphoricacid : potassium =6:38:6, GreenmapII(r), manufactured by Nihon GodohiryoK. K., delivered by Sunscreen K. K.) at 3% by weight were mixed, meltedand mixed, and granulated, so that a material for biodegradable plasticmolded articles was obtained.

The above-described material was molded to raising seedling pots with athickness of 500 μm using an injection molding machine at a processingtemperature of 150° C.

COMPARATIVE EXAMPLE 1

The same biodegradable aliphatic polyester as that in the example at 95%by weight and the coconut powders obtained in the above Productionexample at 5% by weight were mixed, melted and mixed, and granulated, sothat a material for biodegradable plastic molded articles was obtained.

The above-described material was molded to bag shaped films with athickness of 45 μm using a inflation extruder having a diameter of 65 ata processing temperature of 160° C.

COMPARATIVE EXAMPLE 2

The same biodegradable aliphatic polyester as that in the example at 95%by weight and the coconut powders obtained in the above Productionexample at 5% by weight were mixed, melted and mixed, and granulated, sothat a material for biodegradable plastic molded articles was obtained.

The above-described material was molded to raising seedling pots with athickness of 500 μm using an injection molding machine at a processingtemperature of 150° C.

Assessment of Biodegradability

The seedling pots (100 g) in the example, the films (60 g) inComparative example 1, the fragments of the seedling pots (100 g) inComparative example 2, or cellulose powder (100 g) was mixed with 1200 gof soil including leaf soil under the optimum oxygen concentration,temperature, and moisture. These were put into test tubes, allowed tostand at 58° C, and assessed the biodegradability thereof over time(according to a method in ISO DIS 14855). That is, production ratios ofcarbon dioxide and cumulative volumes thereof were monitored for 45days. Biodegradation ratios thereof were calculated based on the solidcarbon amounts of the test substances which were converted into theamounts of carbon dioxide. The results are shown in FIG. 2.

As shown by these results, the seedling pots of the present Example hada higher biodegradation rate than the films or the seedling pots ofComparative examples which had no fertilizer powders, and showed higherbiodegradation rate than the cellulose powder did in about three weekslater. The degradation ratios of the pots were about 80% and about 90%on the 25th day and the 35th day, respectively.

The seedling pots in the example had sufficient physical strength at theinitial time of the biodegradation test.

INDUSTRIAL APPLICABILITY

Since biodegradable plastic molded articles in accordance with thepresent invention have superior biodegradability, they are degraded anddisappear at an early stage, so that they are effective in solving thewaste problems.

What is claimed is:
 1. A biodegradable plastic article molded of amixture comprising the following components: (A) a biodegradable plasticat 98 to 59% by weight, (B) a dry powder of a water-swelling fiber at 1to 40% by weight, and (C) a fertilizer powder at 1 to 40% by weight(wherein the sum of (B) and (C) is from 2 to 41% by weight).
 2. Abiodegradable plastic article as claimed in claim 1, wherein the drypowder of a water-swelling fiber is a dry powder of a coconut mesocarpfiber residue.
 3. A biodegradable plastic article as claimed in claim 1or claim 2, wherein the dry powder of the coconut mesocarp fiber residueis obtained by drying the fiber residue to a water content of about 10%by weight in which the residue is derived from a fiber component of thecoconut mesocarp and a contaminant including a salt and a tannin isessentially removed, by compressing into a powder having a particlediameter ranging from 1 to 80 micron, and by drying to a water contentof less than 3% by weight.
 4. A biodegradable plastic article as claimedin any one of claims 1 to 3, wherein the biodegradable plastic isselected form the group consisting of an aliphatic polyester,macromolecular polysaccharides, and a microbial polyester.
 5. Abiodegradable plastic article as claimed in any one of claims 1 to 4,wherein the fertilizer is selected form the group consisting of anitrogenous fertilizer, a phosphate fertilizer, a potassium fertilizer,and a fertilizer including a diatomaceous.
 6. A biodegradable plasticarticle molded of a mixture comprising the following components: (A) abiodegradable plastic at 97 to 58% by weight, (B) a dry powder of awater-swelling fiber at 1 to 40% by weight, (C) a fertilizer powder at 1to 40% by weight, and (D) a component selected from the group consistingof a surfactant, a pigment, and a pesticide at 1 to 10% by weightwherein the sum of (B), (C), and (D) is from 3 to 42% by weight.
 7. Abiodegradable plastic article as claimed in claim 6, wherein the drypowder of a water-swelling fiber is a dry powder of a coconut mesocarpfiber residue.
 8. A biodegradable plastic article as claimed in claim 6or claim 7, wherein the dry powder of the coconut mesocarp fiber residueis a powder obtained by drying the fiber residue to a water content ofabout 10% by weight in which the residue is derived from a fibercomponent of the coconut mesocarp and a contaminant including a salt anda tannin is essentially removed, by compressing into a powder having aparticle diameter ranging from 1 to 80 micron, and by drying to a watercontent of less than 3% by weight.
 9. A biodegradable plastic article asclaimed in any one of claims 6 to 8, wherein the biodegradable plasticis selected from the group consisting of an aliphatic polyester, amacromolecular polysaccharide, and a microbial polyester.
 10. Abiodegradable plastic article as claimed in any one of claims 6 to 9,wherein the fertilizer is selected from the group consisting of anitrogenous fertilizer, a phosphate fertilizer, a potassium fertilizer,and a fertilizer including a diatomaceous.